In recent years, a technique has been receiving attention in which a semiconductor thin film (a thickness of about a few to a few hundreds nanometers) formed over a substrate having an insulated surface is used to configure TFTs. The TFT is widely used for electronic devices such as ICs and electro-optic devices, which has been urged to develop as a switching device for image display devices.
In addition, an attempt has been made to install various display devices on vehicles such as automobiles and aircrafts, including display devices for navigation systems, operation screen display devices for audio systems, and display devices for meters.
Various applications utilizing such the image display devices are expected, however, attention is being given to the use for portable devices in particular. At present, glass and silica are mainly used for substrates, but the display devices with glass and silica substrates have disadvantages of being thick, heavy-weight and easy to crack, which particularly have disadvantages for portable devices that are highly required to be low-profile, light-weight and hard to crack. Furthermore, glass and silica are generally difficult to be formed into large-sized products, having disadvantages for mass production in particular. On this account, an attempt has been made to form TFT devices on a substrate having bendability, flexibility or elasticity, typically a flexible plastic film or sheet.
However, plastics have low heat resistance, inevitably dropping the maximum temperature in the device fabrication processes. On this account, the electric characteristics of the TFTs formed on a plastic are essentially inferior to the TFTs formed on a glass substrate. Therefore, high-performance light emitting diodes and liquid crystal display devices using plastics have not been realized yet.